The present invention relates to a process for increasing the molecular weight and for the modification of polycondensates, to the use of an additive blend effecting the increase in molecular weight as well as to the polycondensates obtainable by that process and to their use in particular as foam products.
Polycondensates, for example polyamides, polycarbonates or polyesters, in particular polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) as well as polyester copolymers and polyester blends e.g. with polycarbonate (PBT/PC), are important thermoplastics belonging to the group of the engineering plastics. Partially crystalline polyesters are used for injection moulding compounds and are distinguished by high strength and rigidity, high dimensional stability and favourable wear characteristics. Amorphous polyesters have high transparency, superior toughness and excellent stress cracking resistance and are processed, for example, to hollow articles. Another field of application of PET is the production of fibres and foils.
The mechanical and physical properties depend essentially on the molecular weight of the polymer. Polycondensates are prepared by condensation in the melt. Average molecular weights can thus be obtained. For some applications, for example drinks packs and technical fibres, higher molecular weights are necessary. These can be obtained by solid phase polycondensation (S.Fakirov, Kunststoffe, 74 (1984), 218 and R. E. Grxc3xctzner, A. Koine, Kunststoffe, 82 (1992), 284). The prepolymer is in this case subjected to thermal treatment above the glass transition temperature and below the melt temperature of the polymer under inert gas or under vacuum. However, this method is very time-and energy-consuming. Increasing the intrinsic viscosity requires a residence time of up to 12 hours under vacuum or under inert gas at temperatures from 180 to 240xc2x0 C.
According to U.S. Pat. No. 5,235,027 pentaerythritol can also advantageously be added during the solid phase condensation.
WO 98/33837, on the other hand, discloses that the sole addition of pentaerythritol during the reactive extrusion adversely affects the intrinsic viscosity of PET.
Another possibility for obtaining higher molecular weights of polycondensates and, in particular, of polyesters is to add a tetracarboxylic anhydride and a sterically hindered hydroxy-phenylalkylphosphonate, as is disclosed in U.S. Pat. No. 5,693,681. However, a faster increase of the molecular weight at relatively low melt temperatures seems desirable for technical and economical reasons.
It has now been found that the addition of a combination of polyfunctional anhydride, polyfunctional alcohol or phenol and phosphonate with subsequent reactive extrusion of the mixture with a polycondensation polymer or copolymer makes it possible to substantially increase the molecular weight within short reaction times. Surprisingly, the addition of polyfunctional components does not produce any crosslinked polycondensates, but the polyfunctional compounds are essentially incorporated into the chain and result in chain lengthenings and/or branchings.
This is particularly advantageous in the case of used or thermally or hydrolytically damaged polycondensates where the damage typically goes hand in hand with a decrease of the molecular weight. The typical procedure for the processing of PET wastes described in DE 4034459 may be mentioned in comparison.
By means of the process of this invention it is possible to increase the molecular weight, in particular in the case of polycondensate recyclates from useful material collections, such as used packages (foils and bottles) and waste textiles. Recyclates can then be used for high-quality recycling, for example in the form of high-performance fibres, injection moulding articles, in extrusion applications or in the form of foams. Such recyclates originate, for example, also from industrial or domestic useful material collections, from production wastes, such as from fibre production and trimmings, or from obligatory returnables, such as bottle collections of PET drinks packs.
In addition, the physicochemical properties are altered through the process of this invention such that polycondensates can be foamed which normally cannot be easily foamed.
In comparison to unfoamed polymers, foamed polymers have, inter alia, the advantages of material saving, better heat insulation, lower density combined with better mechanical properties. Polymer foams are therefore used in many applications, for example packagings, heat insulation, buffers for the absorption of mechanical forces. Foams consisting of polycondensates meet with growing interest owing to their interesting mechanical properties, their continuous working temperature stability and moulding properties, which are superior to those of other foams.
In comparison to polymers, polycondensates are often characterised by low melt viscosities. At the same time, in particular in the case of polycondensates with aromatic units, there is a marked shear liquefaction during the processing of the polymer melt. This clear dependence of the melt viscosity on the shearing rate goes hand in hand with lower melt elasticities. A sufficiently high melt elasticity is, however, an important precondition for the foamability of polymers. In general, the production of foams from polycondensates is only possible after suitable structural modification.
It is known that, after polycondensation with monomers resulting in amorphous polycondensates, the foamability is improved, as is described, inter alia, in EP 560151. This is the case because the shear liquefaction in the polymer melt is reduced to a certain extent. Owing to aliphatic components, these foams have a lower hydrolytic stability and they are usually biodegradable, i.e. they are not suitable for outdoor use. Moreover, their thermostability is lower. These monomers are furthermore relatively expensive. Amorphous polycondensates are thus not absolutely desirable.
In one of its aspects, this invention relates to a process for increasing the molecular weight and/or for the modification of polycondensates during the processing in the melt, which process comprises adding to the polycondensate a blend comprising
a) at least one polyfunctional anhydride (polyanhydride);
b) at least one polyfunctional compound, the functional groups of which can react with the anhydride groups of component a); and
c) at least one phosphonate.
In addition to polyester, polyamide or polycarbonate, this invention also embraces the corresponding copolymers and blends, for example PBT/PS, PBT/ASA, PBT/ABS, PBT/PC, PET/ABS, PET/PC, PBT/PET/PC, PBT/PET, PA/PP, PA/PE and PA/ABS. However, it needs to be taken into account that the novel process, like all methods allowing exchange reactions between the components of the blend, may influence the blends, i.e. may result in the formation of copolymeric structures.
A preferred process is that wherein the polycondensate is an aliphatic or aromatic polyester, an aliphatic or aromatic polyamide or polycarbonate, or a blend or copolymer thereof.
The polycondensate is particularly preferably polyethylene terephthalate (PET), polybutylene therephthalate (PBT), polyethylenenaphthalate (PEN), polytrimethylene terephthalate (PTT), a copolyester, PA 6, PA 6.6, a polycarbonate containing bisphenol A, bisphenol Z or bisphenol F linked via carbonate groups.
Very particularly preferred polycondensates are PET or a copolymer with PET.
The polycondensate is preferably a recyclate.
Polyamides, i.e. both virgin polyamides and polyamide recyclates, are understood to be, for example, aliphatic and aromatic polyamides or copolyamides which are derived from diamines and dicarboxylic acids and/or of aminocarboxylic acid or the corresponding lactams. Suitable polyamides are for example: PA 6, PA 11, PA 12, PA 46, PA 66, PA 69, PA 610, PA 612, PA 10.12, PA 12.12 and also amorphous polyamides and thermoplastic polyamide elastomers such as polyether amides of the Vestamid, Grilamid ELY60, Pebax, Nyim and Grilon ELX type. Polyamides of the cited type are commonly known and are commercially available.
The polyamides used are preferably crystalline or partially crystalline polyamides and, in particular, PA6 and PA6.6 or their blends, as well as recyclates on this basis, or copolymers thereof.
The polyesters, i.e. virgin polyester as well as polyester recyclate, may be homopolyesters or copolyesters which are composed of aliphatic, cycloaliphatic or aromatic dicarboxylic acids and diols or hydroxycarboxylic acids.
The polyesters can be prepared by direct esterification (PTA process) and also by transesterification (DMT process). Any of the known catalyst systems may be used for the preparation.
The aliphatic dicarboxylic acids can contain 2 to 40 carbon atoms, the cycloaliphatic dicarboxylic acids 6 to 10 carbon atoms, the aromatic dicarboxylic acids 8 to 14 carbon atoms, the aliphatic hydroxycarboxylic acids 2 to 12 carbon atoms and the aromatic and cycloaliphatic hydroxycarboxylic acids 7 to 14 carbon atoms.
The aliphatic diols can contain 2 to 12 carbon atoms, the cycloaliphatic diol 5 to 8 carbon atoms and the aromatic diols 6 to 16 carbon atoms.
Polyoxyalkylene glycols having molecular weights from 150 to 40000 may also be used.
Aromatic diols are those in which two hydroxyl groups are bound to one or to different aromatic hydrocarbon radicals.
It is also possible that the polyesters are branched with small amounts, e.g. from 0.1 to 3 mol %, based on the dicarboxylic acids present, of more than difunctional monomers (e.g. pentaerythritol, trimellitic acid, 1,3,5-tri(hydroxyphenyl)benzene, 2,4-dihydroxybenzoic acid or 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane).
Suitable dicarboxylic acids are linear and branched saturated aliphatic dicarboxylic acids, aromatic dicarboxylic acids and cycloaliphatic dicarboxylic acids. Suitable aliphatic dicarboxylic acids are those containing 2 to 40 carbon atoms, for example oxalic acid, malonic acid, dimethylmalonic acid, succinic acid, pimelic acid, adipic acid, trimethyladipic acid, sebacic acid, azelaic acid and dimeric acids (dimerisation products of unsaturated aliphatic carboxylic acids such as oleic acid), alkylated malonic and succinic acids such as octadecylsuccinic acid.
Suitable cycloaliphatic dicarboxylic acids are: 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3- and 1,4-cyclohexanedicarboxylic acid, 1,3- and 1,4-(dicarboxylmethyl)cyclohexane, 4,4xe2x80x2-dicyclohexyldicarboxylic acid.
Suitable aromatic dicarboxylic acids are: In particular terephthalic acid, isophthalic acid, o-phthalic acid, and 1,3-, 1,4-, 2,6- or 2,7-naphthalenedicarboxylic acid, 4,4xe2x80x2-diphenyidicarboxylic acid, 4,4xe2x80x2-diphenylsulfonedicarboxylic acid, 4,4xe2x80x2-benzophenonedicarboxylic acid, 1,1,3-trimethyl-5-carboxyl-3-(p-carboxylphenyl)indane, 4,4xe2x80x2-diphenyl ether dicarboxylic acid, bis-p-(carboxylphenyl)methane or bis-p-(carboxylphenyl)ethane.
The aromatic dicarboxylic acids are preferred, in particular terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid.
Other suitable dicarboxylic acids are those containing xe2x80x94COxe2x80x94NH-groups; they are described in DE-A2414349. Dicarboxylic acids containing N-heterocyclic rings are also suitable, for example those which are derived from carboxylalkylated, carboxylphenylated or carboxybenzylated monoamine-s-triazinedicarboxylic acids (viz. DE-A-2121184 and 2533675), mono- or bishydantoins, optionally halogenated benzimidazoles or parabanic acid. The carboxyalkyl group can in this case contain 3 to 20 carbon atoms.
Suitable aliphatic diols are the linear and branched aliphatic glycols, in particular those containing 2 to 12, preferably 2 to 6, carbon atoms in the molecule, for example: ethylene glycol, 1,2- and 1,3-propylene glycol, 1,2-, 1,3-, 2,3- or 1,4-butanediol, pentyl glycol, neopentyl glycol, 1,6-hexanediol, 1,12-dodecanediol. A suitable cycloaliphatic diol is e.g. 1,4-dihydroxycyclohexane. Other suitable aliphatic diols are e.g. 1,4-bis(hydroxymethyl)cyclohexane, aromatic-aliphatic diols such as p-xylylene glycol or 2,5-dichloro-p-xylylene glycol, 2,2-(xcex2-hydroxyethoxyphenyl)propane and also polyoxyalkylene glycols such as diethylene glycol, triethylene glycol, polyethylene glycol or polypropylene glycol. The alkylene diols are preferably linear and preferably contain 2 to 4 carbon atoms.
Preferred diols are the alkylenediols, 1,4-dihydroxycyclohexane and 1,4-bis(hydroxymethyl)-cyclohexane. Particularly preferred are ethylene glycol, 1,4-butanediol and 1,2- and 1,3-propylene glycol.
Other suitable aliphatic diols are the xcex2-hydroxyalkylated, in particular xcex2-hydroxyethylated, bisphenols such as 2,2-bis[4xe2x80x2-(xcex2-hydroxyethoxy)phenyl]propane. Other bisphenols will be mentioned later.
Another group of suitable aliphatic diols are the heterocyclic diols described in DE-A-1812003, DE-A-2342432, DE-A-2342372 and DE-A-2453326, for example: N,Nxe2x80x2-bis(xcex2-hydroxyethyl)-5,5-dimethylhydantoin, N,Nxe2x80x2-bis(xcex2-hydroxypropyl)-5,5-dimethylhydantoin, methylenebis[N-(xcex2-hydroxyethyl)-5-methyl-5-ethylhydantoin], methylenebis[N-(xcex2-hydroxyethyl)-5,5-dimethylhydantoin], N,Nxe2x80x2-bis(xcex2-hydroxyethyl)benzimidazolone, N,Nxe2x80x2-bis(xcex2-hydroxyethyl)-(tetrachloro)benzimidazolone or N,Nxe2x80x2-bis(xcex2-hydroxyethyl)-(tetrabromo)benzimidazolone.
Suitable aromatic diols are mononuclear diphenols and, in particular dinuclear diphenols carrying a hydroxyl group at each aromatic nucleus. Aromatic will be taken to mean preferably hydrocarbonaromatic radicals, such as phenylene or naphthylene. Besides e.g. hydroquinone, resorcinol or 1,5-, 2,6- and 2,7-dihydroxynaphthalene, the bisphenols are to be mentioned in particular, which can be represented by the following formulae: 
The hydroxyl groups can be in m-position, preferably in p-position, and Rxe2x80x2 and Rxe2x80x3 in these formulae can be alkyl containing 1 to 6 carbon atoms, halogen, such as chloro or bromo, and, in particular, hydrogen atoms. A may be a direct bond or xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94(O)S(O)xe2x80x94, xe2x80x94C(O)xe2x80x94, xe2x80x94P(O)(C1-C20alkyl)-, unsubstituted or substituted alkylidene, cycloalkylidene or alkylene.